title: Postnatal changes in the developing rat extraocular muscles.
abstract: OBJECTIVE
  To examine the distribution and timing of expression of nonmuscle myosin IIB (nmMyH IIB) and the extraocular muscle (EOM)-specific myosin (EO-MyHC) during postnatal development of the rat extraocular muscles.
  
  
  METHODS
  Whole orbits were collected from postnatal development day (P) 1 through P30 from Sprague-Dawley rats. Samples were analyzed by immunofluorescence microscopy and Western blot to examine the distribution and abundance of nmMyH IIB and EO-MyHC compared with other myosin isoforms and sarcomeric α-actinin. Polyclonal antibodies were produced to specifically detect EO-MyHC. Postnatal limb muscles were used as control.
  
  
  RESULTS
  Analysis of EOM morphology in the developing orbits indicates that the global and orbital layers are not evident until day P15. The distribution of nmMyH IIB changes between days P10 and P15 from a subsarcolemma distribution to an intrafiber distribution in the global layer. EO-MyHC appears by day p15, primarily in the orbital layer of the EOMs. Sarcomeric α-actinin was equally abundant in the EOMs at all stages. Fetal MyHC was the predominant isoform at day P1 but slowly diminished in abundance with age in a layer-specific manner.
  
  
  CONCLUSIONS
  These data demonstrate that significant changes occur in the EOMs from P10 to P15 and suggest that visual stimulation may play a role in the signals that regulate both nmMyH IIB and EO-MyHC developmental transitions. The pronounced distinctions of the orbital and global layers occurring by P15 establish the adult morphologic phenotype of the muscle.
authors.affiliation: Department of Molecular and Cellular Biochemistry, University of Kentucky, Lexington, Kentucky 40536, USA. cmonc2@uky.edu
authors.forename: Carole L
authors.initials: CL
authors.lastname: Moncman
authors.forename: Miguel E
authors.initials: ME
authors.lastname: Andrade
authors.forename: Francisco H
authors.initials: FH
authors.lastname: Andrade
mesh_terms: D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn; D005260:Female; D007150:Immunohistochemistry; D018485:Muscle Fibers, Skeletal / Q000378:metabolism; D018995:Myosin Heavy Chains / Q000378:metabolism*; D024501:Nonmuscle Myosin Type IIB / Q000378:metabolism*; D009801:Oculomotor Muscles / Q000166:cytology / Q000254:growth & development* / Q000378:metabolism*; D011247:Pregnancy; D051381:Rats; D017207:Rats, Sprague-Dawley; D012508:Sarcolemma / Q000378:metabolism
chemical_list: C000594638:MYH7 protein, rat; D024501:Nonmuscle Myosin Type IIB; D018995:Myosin Heavy Chains